The present invention relates to a radiation image reading apparatus, and particularly to a radiation image reading apparatus which is used in a radiation image information recording and reproducing system using a radiation detector.
From the past, a radiation image represented by an X-ray image is widely used for the disease diagnosis. As a method to obtain the radiation image, so-called radiography system by which the radiation which passes through the subject is irradiated onto a fluorescent substance layer which is called an intensifying screen of the radiation detector, and a visible ray emitted from this fluorescent substance layer is irradiated onto the a silver halide photosensitive material (hereinafter, called “photosensitive material”), and a developing processing is conducted on this photosensitive material and a visible image is obtained, is proposed and put into practical use.
In recent years, instead of the radiography system, a radiation image recording and reproducing system in which the irradiated radiation energy is accumulated and recorded, and the radiation detector having a “stimulable phosphor” which stimulably emits corresponding to the accumulated and recorded radiation energy, when exciting light is irradiated, is used, is proposed. This system is structured in such a manner that, when the radiation transmitted the subject, is irradiated onto the sheet-like stimulable phosphor, after the radiation energy (hereinafter, called “image information”) corresponding to the radiation transmittance density of each portion of the subject, is accumulated and recorded into the stimulable phosphor, the image information accumulated and recorded in the stimulable phosphor is emitted by the exciting light as the stimulable emission light, and the intensity of this stimulable emission light is converted into an electric signal, and through the image recording material such as the photosensitive material or an image display apparatus such as a CRT, it is reproduced as a visible image.
Sheet-like stimulable phosphor (hereinafter, called “stimulable phosphor sheet”) 500 is, as shown in FIG. 37, in many cases, arranged in a housing 520 in the condition that it is fixed on a predetermined supporting plate 510, and used for the radiation image radiographing, and after the radiation image radiographing is completed, the image information accumulated in the stimulable phosphor is read out by a radiation image reading means (hereinafter, called “reading means”) 530 provided in the housing 520. The radiation image radiographing apparatus provided with such a reading means 530 is called the “radiation image reading apparatus”.
As the reading means 530, as shown in FIG. 37, a means arranged on the rear surface side (opposite side to the radiation source) of the stimulable phosphor sheet 500 is proposed, and put in practical use. This reading means is provided with an exciting light source 531, light guiding means 532, and photoelectric conversion means 533, and the image information accumulated on the stimulable phosphor sheet 500 is emitted as the stimulable emission light from the rear surface side by the exciting light irradiated from the exciting light source 531, and the stimulable emission light is guided to the photoelectric conversion means 533 through the light guiding means 532 and converted into an electric signal. This electric signal is transferred to an image processing means, not shown, and the image processing is conducted, and visualized.
When the radiation image reading apparatus provided with the reading means 530 which reads out the stimulable emission light emitted from the rear surface side (opposite side to the radiation source) of such the stimulable phosphor sheet 500, is used, there is a following problem.
That is, on the radiation source 600 side of the stimulable phosphor sheet 500, as shown in FIG. 38, there exist the subject, front plate 521 of housing 520, and supporting plate 510 (in the order from the radiation source 600), and stimulable phosphor sheet 500 accumulates also the radiation (scattering ray) of the low energy scattered when the radiation passes through them. When the accumulation of the accurate image information is hindered by such the scattering ray, there is a case where various harmful influences such as the lowering of the diagnostic performance are caused.
Particularly, when the subject 700 is arranged above such a radiation image reading apparatus and the radiographing is conducted (that is, in the case of the radiographing at the “lying position”), because it is necessary that a top board 800 supporting the weight of the subject 700 is provided between the subject 700 and the front plate 521 of the housing 520 (refer to FIG. 39), a bad effect in which the scattering ray gives to the radiation image, is larger.
As a means for shielding such the scattering ray, conventionally, a “grid” structured in such a manner that a laminating body in which a radiation absorption layer formed of lead having the high radiation absorption factor and a radiation transmitting layer formed of aluminum, paper, wood, and synthetic resin which have the low radiation absorption factor are alternately provided, is covered by a cover member having the low radiation absorption factor, is used, and the scattering ray is shielded by arranging the grid in the vicinity of the subject 700 side.
However, because there is a case where the radiation is scattered also by a member constituting the grid or grid itself, there is a case where the accurate accumulation and recording of the image information which reaches the stimulable phosphor sheet are hindered.
Further, in the recent years, instead of the radiography system, a radiation image radiographing system by which the radiation detector such as a semiconductor sensor is used and the radiation image is radiographed, the radiation image is converted into the electric signal (image signal), and the electric signal (image signal) is image-processed and displayed on the CRT, is proposed.
A radiation image radiographing apparatus used in the radiation image radiographing system is, generally, provided with the housing fixed at a predetermined position and the radiation detector housed in this housing, and the radiation which is irradiated from the radiation source and passing through the subject and the front plate of the housing, is detected by the radiation detector. The radiation detector is provided with the conversion means for converting the detected radiation into the electric signal (image signal), and the electric signal (image signal) converted corresponding to the level of the detected radiation is sent to the image processing means, and herein, a predetermined image processing is conducted and it is outputted to the image display means such as the CRT, and displayed.
According to the radiation image radiographing system using the radiation image radiographing apparatus, the very broader range radiation can be detected as compared with the radiographing method, and the radiation image with an abundant amount of information can be obtained.
However, the radiation detector housed in the radiation image radiographing apparatus detects even the radiation (scattering ray) of the low energy scattered on each kind of members until the radiation is absorbed in the radiation absorption layer and detected. When the detection of the accurate image signal is hindered by such the scattering ray, there is a case where the various harmful influences such as the lowering of the diagnostic performance are caused.
The object of the present invention is to provide a radiation image radiographing apparatus by which the scattering ray is effectively shielded, and the image quality of the radiation image can be largely increased.